Unless you changed the installation path for the Java Development Kit or the Java Runtime Environment during installation, it will be in a directory under C:\Program Files\Java for a 32 bit architecture and under c:\Program Files (x64) for a 64 bit Windows system. Using Explorer, open the directory C:\Program Files or Program Files (x64) \Java.
Inside that path will be one or more subdirectories such as jdk1.5.0_08. If you have just installed the Java Development Kit, it will be installed to the newest directory, which you can find by sorting by date. For example, it may be installed in C:\Program Files\Java\jdk1.5.0_08. This is the installation path.
An example of an installation path for the JRE on a 64 bit windows system would be c:\Program Files(x64)\java\jre6

Set the JAVA_HOME or JRE_HOME Environment Variable

Once you have identified the JDK installation path:

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